Ampli



April 10, 1928 r 1,665,501 J. S. JAMMER AMPLIFYING REPEATER Filed May22. 1923 I l I l I l l l I l I hue/WW: I Jaca J. Jammer Patented Apr.10, 1928.

UNITED STATES 1,665,501 P TEN OFFICE.

. JACOB s. JAMMER, on NEW YORK, N. ASSIGNOR T0 WESTERN ELECTRIC COMPANY,INGORPDRATED, OF NEW roan, N. Y., A CORPORATION on NEW YORK.

AMPLIF ING nnrna rnni Application filed May 22,

This invention relates to an amplifying repeater such as employed inmultiple); car rier current telephone and telegraphsystems whereindiflferent channel frequencies for transmission in one direction aregrouped in a different frequencyrange from that employed fortransmissionin the opposite direction. p 1

Among the objects of the invention are:

To produce a two-way amplifying repeater wherein the amplifiers foroppositely directed transmissions have different amplityingcharacteristics.

To produce a tWo-wayamplifying repeater wherein the amplifyingcharacteristics of the amplifiers for oppositelydirected transmissionsare particularly suited to the frequency range of the currents to heamplified therefier for the transmitted currents of the lowerfrequencies.

To produce an elficient and economical two-Way repeater.

The invention is illustrated as applied to a two-way amplifying repeaterfor use in a multiplex carrier current telephone and telegraph system,but itis to be understood that it may also he applied to two-wayamplifying repeaters for use in other signaling systems wherein thefrequencies of the Waves transmitte din one direction are in a differentfrequency range thanthat embracing the waves transmitted in theoppositedirection.

In the drawing- "Fig.1 illustrates diagrammatically a two-- wayamplifying repeater having a two-stage amplifier for the group of higherfrequency wares and a single stage amplifier for the group of lowerfrequency waves.

Fig. Qillustrates diagrammatically a twoway amplifying repeater having asingle stage amplifier for each group, the ampli" tying factor of oneheinggreater than that of the other. e Fig. 3 shows curves representingthe ant plifying"characteristics of the amplifiers of Figures" land 2. eFig. lrepresents the gains ofthe respective amplifiers of the two-wayrepeaters shown in Figs. 1 and 2. p

The two-way repeater of Fig. l, compris- 1923. seriarNo. 640, 43.

ing two one-way repeating channels RE and RVV, is adapted to couple twotransmission line sections E and 7.

The currents incoming to the repeater station from line section E areamplified in the repeating channel RE and the amplified currents aredelivered to line section V. Likewise, the. currents incoming from linesection W are amplified in the repeating channel RVV and the amplifiedcurrents are delivered to line section E. e

The currents incoming from the line section W are of higher frequenciesthan those incoming from line section E, and, as will more fullyhereinafter appear, the respective repeating channels are provided withfrequency discriminating filters which direct the incoming currents tothe proper channel.

It is Well known that the characteristics of a line are such thattheattenuation of the currents traversing it increaseswith an in creaseof frequency. The attenuation per unit length of line will, therefore,be greater for the currents incoming from line section V, than for thoseincoming from line section E.

Since the repeater is for the purpose of amplifying the attenuatedcurrents and it is desirablethat the outgoing transmissions of allfrequencies from the repeater be at substantially the same energy levelthe attenuated currents of the higher frequencies.

. means having amplifying factors selected in accordance with thefrequencies of the currents to he amplified are Reduction in number andcost of amplifiers. e Reduction incest of directional filters employedin the repeating channels.

The repeating channel RE includes input.-

and output filters, EIF and EOF, an amplifier EA and an attenuationequalizer The input and output filters EIF and 357 granted April 18,1922.

EOF may be low pass filters of the type disclosed in the patei'it toltaibonrn, No. 1,t13,-

They are designed to pass currents of the frequencies to be amplifiedinthe repeater channel RE and to suppress currents of higherfrequencies.

The amplifier EA. may be of any well known type, but, as illustrated, isof the balanced type somewhat similar to that disclosed in Fig. l of U.patentto' Colpitts, No. 1,128,292 granted February 16, 1915, but it mustbe adapted to handle the wide range of frequencies encountered in amultiple-X carrier current system.v

The input current to the amplifier EA may be regulated by apotentiometer 1.

The attenuationequalizer EAE, comprising an inductance 2 shunted by acapacity 3 connected in series with resistances at and 5, serves to soterminate the input filter Ell? as to equalize the differences in lineattenuations at the different frequencies of the currents to beamplified by amplifier EA. -Thus the outputs from the amplifier are ofsubstatially equal value for the different frequencies.

The repeating channel It? includes input and output filters VVIF andVVOF, two amplifielj's WA and IVA connected in tandem by an inter-stagefilter ISF, and an attenuation equalizer \VAE. The input and outputfilters .VIF and 0F may be high pass filters of the type disclosed inthe Raibourn patent, supra. They are designated to pass currents of thefrequencies to be amplified in the repeating channel Riv and to suppresscurrents of lower frequencies. The interstage filter ISF is of the sametype as the high pass filters WIE and WOF and passes only currents ofthe frequencies passed by these in- I put and output filters.

A two-stage amplifier. wherein the twoamplifying structures areconnected by a directional filter is disclosed and claimed in mycopending' applicationSerial No. 616,- 243, filed February ,1, 1923.

The amplifiers A and VVA which are similar to amplifier EA, formatwo-stage amplifier which has an amplifying factor greater than that ofthe single stage amplifier EA.

The input current to the amplifier We. 1 maybe regulated by apotentiometer 6.

The attenuation equalizer VVAE is similar to the equalizer EAE andserves the same general purpose.

Of course should occasion require it, additional stages of amplificationmaybe introduced into each repeating channel.

The repeater of Fig. 2v is similar tothat of Fig. 1, differing therefromprincipally in that but a .single stageamplifier is employed in'eachrepeating channel. These amplifiers, however, are so construct cd thatinherently the amplifying factor of the west amplifier A is greater thanthat of the east amplifier E A.

ll hether an electronic valve amplifier has a high or low amplifyingfactor depends upon the construction of the control electrodeor grid andthe spacing of the grid with respect to the cathode.

Thus an electronic amplifier having a grid of fine mesh spacedrelatively close to the cathode has a high amplifying factor. lf thegrid is of coarse mesh and spaced farther from the cathode, theamplifying factor will be lower.

Fig. 3 shows curves illustratiin the diftierence in anngilifyingclniractcris east and west amplifiers employed. in the repeaters shownin F l and 2.

These curves are obtained by plotting the input voltage E as abscisszeagainst the out put current L as ordinates.

Curve A represents the an'iplifying characteristic or factor of the westamplifier which amplifies the higher frequency cur rents, and curve Bthe amplifying characteristic or factor of the east amplifier whichamplifies the lower frequency currents.

In Fig. the line CD represents the attenuation characteristic of atransmission line section of approximately 250 miles of open wire No. 8Bil G line for frequencies from (5.7 to kilocyclcs. This line Cl) alsorepresents the necessary net gain of the two-way repeater to compensatefor the line attenuation.

Where the transmissions in omiositc directions in a carrier telephonesystem are grouped, the channel frequencies for one direction may liewithin the frequency range of 6.7 to 19 kilocycles and the channelfrequencies for the opposite direction may lie within the frequencyrange of 21 to tit-3.3 kilocycles.

, Inspection of Fig. 4 shows that currents of frequencies within theupper group of 21 to kilocycles are attenuated more more than currentshaving frequencies within the lower group. conscrpiently, a lower netgain is required of the repeating channel handling the lower frequencygroup than is required of the repeating channel handling the upperilrequency group.

The gross amplification of each. repeating channel must be such as tocon'ipcnsatc for the attenuation of the highest frequency currentshandled thereby. V

Thus, the amplifier of the repeating channel Bil provides a gross gainrepresented by the area DEFG. The attenuation equalizer XVAE introducesa loss represented by the area DEH thereby leaving the net gain ofv thewest repeating channel equivalent to the area DHFG.

The amplifier or the repeating channel RE provides a gross gainrepresented by the area JKLM. The attenuation equalizer EAE introduces aloss represented by the area CJK. Consequently, the net gain is siblesinging of the repeater. This loss is caused principally byattenuationwhich (the filters produce in currents outside theirtransmission range.

According to the usual practice, two-way repeaters are constructed sothat the gross gain of each repeatingchannel is the same. Since the netgain for the two repeating channels is not the same, it is necessary,according to present practice, to introduce a loss in the channel ofwhich the lower net gain is required, which means ordinarily that thisrequired additional loss must be introduced by the filters or othermeans, thereby increasing materially and unnecessarily the cost oftherepeater.

According to the present invention, each repeating channel provides onlythe gross galn necessary tocompensate for the attenuation of the highestfrequency currents within the group handled thereby. Consequently,theloop gain is lower than in repeaters as previously employed. While theloop loss must exceed the loop gain to prevent sin in less loss is reuired b the repeater embodying the present invention. This loop loss isintroduced by the filters "which may be less expensive as less energy isto be dissipated.

The invention set forth herein is, of course, susceptible of variousother embodiments and adaptations.

The invention claimed is:

l. The combination of a transmission line for transmitting in oppositedirections a plurality of carrier currents comprised in re spectivefrequency ranges, said line having greater attenuation for Waves ofhigher frequency transmitted in one direction than for Waves of lowerfrequency transmitted in the opposite direction, and a two-way repeatercomprising oppositely directed transmission paths, each path includingmeans to select a group of carrier currents, an a1nplifying means and anequalizer for compensating for the unequal attenuation produced by theline in the waves of the different frequencies comprised in therespective frequency ranges, the amplifying means in the pathtransi'nitting the waves of the higher frequencies having a greateramplifying factor than that in the path transmitting thewaves of thelower frequencies, each amplifying means having an' amplifying factorsuch that the net gain over the loss introduced by the entire circuitincluding the line and respective equalizer is substantially the samefor each frequency transmitted over the system. i

2. A two-way repeater for coupling two transmission lines over which thecurrents transmitted in. one direction are of higher frequencies thanthose transmitted. in the opposite direction, comprising two asymmetricrepeating channels, input and output filters in each of said channels,an amplifier connected between the input and output filters in each ofsaid channels, and equalizers in the respective channels for equalizingthe differences in line attenuation in the different frequencies tobeamplified by each repeater, the amplifying factor of the amplifier inthe higher frequency channel being greater than that of the otherchannel to effect the same net amplification in the higher frequencyrepeater channel and the line therefor and in the lower frequencyrepeater channel and the line therefor.

In witness whereof, I hereunto subscribe my name this 18th day of May A.D., 1923.

JACOB S. JAMlMER.

